Temperature-induced change in the ESR spectrum of the Fe3+ ion in polyaniline

Research on polyaniline doped with K3[Fe(CN)6] has revealed an effect which is manifested in an unusual temperature-induced change in the ESR spectrum of the Fe3+ ion. At low temperature (T=4.2 K) one observes the first resonance line (g1=4.22±0.03), and at high temperature (T=295 K) the second line (g2=2.13±0.05). The transition from the low-to the high-temperature spectrum occurs gradually and is accompanied by a redistribution of the absorption intensity. The observed properties of the temperature dependence of the ESR spectrum are typical of systems with a multiple-minimum potential.